Project Summary Vectorial capacity of American triatomines for multiple strains of Trypanosoma cruzi Chagas disease, caused by infection with the parasite Trypanosoma cruzi, is a lifelong, life- threatening infection affecting over eight million people worldwide. Blood-feeding insects of the family Triatominae, also called kissing bugs, transmit T. cruzi during or shorty after a blood meal when infected bug feces enters the bite wound or a mucous membrane. Triatomines occupy diverse habitats from the southern cone of South America through the southern United States. Much remains unknown about key components of North American triatomine behavior and biology that determine the likelihood of human disease transmission. This proposal uses experimental infections of laboratory populations of three epidemiologically important North American triatomine species to determine their susceptibility to infection with native parasite strains. Further, the feeding and defecation behavior of these species are used as a measure of transmission probability?the more quickly the triatomine defecates while taking a blood meal, the more likely transmission is to occur. These measures will parameterize a model of vectorial capacity, which measures the risk presented by vectors to human exposure. The development of this analytical framework is critical to the identification of environmental characteristics leading to increased spillover to humans, and targeting vector control efforts towards the vector and vertebrate species most likely to transmit T. cruzi to humans.